1. Field of the Invention
The present invention relates in general to the field of cooking appliances. More particularly, the present invention relates to an adjustable downdraft ventilator for a cook top that may be electronically controlled.
2. Discussion of the Related Art
Historically, adjustable telescoping ventilators for cook tops are well-known to those skilled in the art. Conventional telescoping downdraft ventilators are typically long rectangular boxes having an inner telescoping box and outer base box of single walled or a double walled construction with insulating air in between. The telescoping rectangular box generally has an opening to the interior of the base box for exhausting. A top trim cap of the telescoping rectangular box is fixed in a horizontal plane and often flush with the counter when retracted. A blower system preferably has a single blower and is attached on the side of the base box with airflow at 90 degrees. The blower is designed to draw air downwardly away from the cook top to remove contaminated air from a cook top surface to the interior of the box where it is then exhausted, preferably outside. The blower may be a centrifugal fan or an axial fan.
While the centrifugal fan creates higher pressures than that of an axial flow fan, the air stream has to turn 90 degrees once inside the chamber to move downward. The air stream has to then turn 90 degrees again into a small diameter opening when compared to the size of the ventilator's chamber. Once the air stream has entered the blower region, the centrifugal fan/blower redirects it again downwardly and outwardly for exhausting. With all this bending of the air stream, large amounts of draw/vacuum/suction is needed to overcome all these losses. With the need for more draw/vacuum/suction comes a large motor, which increases costs, noise, size, and weight.
Centrifugal fans or blowers of prior designs consist of a wheel with small blades on the circumference and a shroud to direct and control the airflow into the center of the wheel and out at the periphery. The blades move the air by centrifugal force, literally throwing the air out of the wheel at the periphery, creating a vacuum/suction inside the wheel. The basic design of wheel blades in centrifugal blowers consists of forward curved and backward inclined blades.
Forward curved wheels are operated at relatively low speeds and are used to deliver large air volumes against relatively low static pressures. However, the inherently light construction of the forward curved blade does not permit this wheel to be operated at speeds needed to generate high static pressures and is generally not used in telescoping downdraft ventilators for that reason.
The backward inclined blower wheel design has blades that are slanted away from the direction of the wheel travel. The performance of this wheel is characterized by a high efficiency, high cubic feet per minute (CFM) flow and is usually of rugged construction making it suitable for high static pressure applications. The maximum static efficiency for these types is approximately about 75 to 80%. A draw back to this type is that it needs to be designed for twice the speed (for ruggedness) that increases the cost of the unit.
Axial flow fans are generally not used for telescoping downdraft ventilator as they do not provide the static pressures needed for the drawing/vacuum/suction, size, and spacing requirements. Axial flow fans typically come in three basic types of fans. The propeller fan (the house hold fan), the tube axial fan, and vane axial fan (cross flow or tangential). The propeller is the most familiar and consists of a propeller blade and an associated aperture to restrict blow back from the sides. Without the aperture, the fan is not truly a propeller fan, since it cannot positively move air from one space to another. The aperture is usually designed of sheet metal/plastic and fits closely around the periphery of the propeller. The tube axial fan (e.g., the type found in computers) is literally a propeller fan in a tube. In this case, the tube replaces the aperture. The tube increases flow quantity, pressure and efficiency, due to the reduced air leakage at the blade tips. The vane axial fan (sometimes referred to as a cross flow or tangential fan) is a tube axial fan with the addition of vanes within the tube to straighten out the air flow. The air flow changes from helical flow imparted by the propeller into a more nearly straight line flow and in the process increases the pressure and efficiency while reducing noise.
In general, the propeller fan operates at the lowest pressure. The tube axial fan's pressure is somewhat higher. The vane axial fan supplies the highest-pressure output of the three. Vane axial fans are noted for use when available space for installation is limited, such as for computers. Static efficiencies of 70 to 75% are achieved with vane axial fans. The CFM and static performance range of the vane axial fan is similar to that of a centrifugal fan and horsepower requirements are about the same for both designs.
Most present telescoping downdraft ventilators use centrifugal type fans/blowers. Thus, as mentioned, the airflow is drawn in at a 90 degrees bend from a small opening at the cook surface, and then bends 90 degrees again to the fan. This bending of the airflow reduces the air draw/vacuum/suction effectiveness of a telescoping downdraft ventilator using a centrifugal fan/blower and results in poor venting performance. Also a big issue with centrifugal fans/blowers is the noise. These units are very loud and users find this to be a problem when using present telescoping downdraft ventilators.
Another issue is that current telescoping downdraft ventilators of present designs stop only at full up (open) and full down (closed) and use mechanical or tactile type controls to control and operate the removal of air and the stop points of the up and down movement. These mechanical/tactile type controls are inaccurate and often do not work properly. Present designs use knobs and slides to set and control mechanical switches for setting the desired speed and stops. These types of products provide inaccuracies and other operating problems in an often dirty, hot, and sticky working environment. Further, they have problems maintaining a set point partly due to the design of the telescoping downdraft ventilator and method of drawing air, but also do to the inaccuracy of the mechanical switches themselves. Mechanical control switches often suffer from hysteresis, which contributes to their inaccuracies in the controllability to hit a set point or repeat a function. Moreover, because they operate in an environment consisting of heated air, steam, oils, greases, particulates and effluents, without proper protection these switches fail by working too slowly, cracking, discoloring, becoming harder to turn, failing to operate, chattering, and failing in repeatability. Moreover, if mechanical switches and/or controls are used on cook tops in outdoor environments like rain, snow, sun, and UV, special sealings are required to prevent intrusion of these environmental conditions and premature failure or reduced product life. The need for special sealed controls used in these environments increases the price of a telescoping downdraft ventilator that is used outdoors.
Present design telescoping downdraft ventilators that use linear tactile electronic controls have tactile type switches with a membrane pad over them for controlling the functions. Tactile switches for this use often have an extension that causes the switch to stick out so the user can properly operate the unit. This causes the user to press hard in order to use the rubber or other plastic like buttons. In the manufacturing process of these tactile switches, contamination can enter the space, which over time causes problems for the user and sometimes results in failure. Further, environments having grease, heat, odor, particulates, and other fluids may cause any type of gap to be filled with contamination. Thus, adding an extension to any switch can cause problems for the user both in a build up of contamination but also in the ability to clean.
To date, present telescoping downdraft ventilators have not used sensors to detect the presence of temperature, etc. Further, no proper airflow detection method has been provided to indicate to the user it is time to change the filter. In fact, some of the filters, on some designs are hidden from view. Other manufactures have a run time setting to indicate when the filter should be removed, however, this does not detect if filter is truly plugged. For the heavy user, the filter needs cleaning sooner and this feature is a problem. For the light user, while a metal mesh filter can be washed and replaced, frequent replacement of a disposal filter can get costly.
Some present designs are also limited to islands only, primarily due to their bulky size. With the present units built into an island, the ability to provide light is a problem for the user. While overhead range hood-type units provide lighting from above, such telescoping downdraft ventilators do not provide lighting. Thus, the user has problems using this product.
Other issues are presented with present telescoping downdraft ventilators stemming from the height that the unit extends up from the counter top. Some units extend up only 7 inches, where others only 15 inches with no adjustability for height. The low extending units provide no effective draw when a large tall pot is place on a burner. On the other hand, the units that extend 15 inches provide limited effectiveness when the user uses a low fry pan. Again no adjustment can be made for height. On some of the large fixed height units (15 inches), large filters are used. These now cause problems because the drawing air can extinguish the gas flame. On ranges with auto sparking for relighting of the gas burners, reports from the use of these ventilators describe continued sparking from these units because the relighting module remains on. No present units provide varying heights, which would reduce these problems.
Issues also remain with the present telescoping downdraft ventilator moving smoothly up and down. Some use a scissor mechanism which jams up, binds, or fails to operate. Moreover, they jerk up and down and stop in between movements. Mechanical switches used to detect stopping points for both up and down are plagued with reliability problems. Screw drives have been used on high end telescoping downdraft ventilators, but again have problems with mechanical switches and levers. For example, the switches and levers cannot detect obstructions during travel up and down. Further, these problems and failures increase the cost of manufacture and maintenance.
Present designs are also often large and bulky. However, for a telescoping downdraft ventilator built into a cabinet or in an island, the space below the unit is limited especially for a user to use. This is due to the size of the centrifugal blower, and the size of the base housings presently used. Size also limits the telescoping downdraft ventilator from being placed in other areas and limits the telescoping downdraft ventilator from being used as a freestanding unit, as a mobile unit, used in a cabinet (e.g. suspended), or in areas that do not have the ability to support a large structural frame.
What is needed therefore is a ventilator with a better airflow that is easier to control. There also exists a need for a state of the art telescoping downdraft ventilator in which accurate controlled speed, venting, and removal of contaminates is accomplished. Further, there exists the need for an accurate method of sensing and controlling the ventilator's operations and settings. There also exists a need for control(s) to be less susceptible to the environment. There exists a need for the user to be able to view the operation(s), speed(s), set point(s) functions, view the contents on the cook top, and a need for a remote control or controls that do not use tactile switches. There is a further need to accurately apply and control the height for a new design such that it can be used in other limited spaces and places.
A preferred solution will also be seen by the end-user as being cost effective. A solution is cost effective when it is seen by the end-user as compelling when compared with other potential uses that the end-user could make of limited resources.